1. Field of the Invention
The present invention relates to a method for producing a conductive polyaniline and an organic polymer composition containing the same. More particularly, it relates to a method for producing a conductive polyaniline stably dispersed in an organic solvent and having a high electroconductivity and an organic polymer composition containing the same. The present invention also relates to a conductive substrate formed from a dispersion of the above conductive polyaniline having a high electroconductivity and stably dispersed in an organic solvent as well as a photovoltaic device and dye-sensitized solar cell using the same.
2. Description of the Related Art
It is known to obtain a conductive polymer including electrolyte ions as a dopant by chemical oxidative polymerization of aniline or an aniline derivative. However, conductive polyaniline is generally insoluble in an organic solvent and also is non-meltable, and therefore, is poor in processability and difficult to develop applications thereof. Further, it has been reported to obtain polyaniline and polyaniline derivatives soluble in an organic solvent by polymerization of a salt of an aniline comprising sulfonic acid such as dodecylbenzene sulfonic acid, dinonylnaphthalene sulfonic acid and aniline or its derivative (Japanese Unexamined Patent Publication (Kokai) No. 6-279584 No. 2003-176409, U.S. Pat. No. 5,232,631). However, the solubility of polyaniline or a polyaniline derivative in an organic solvent is not necessarily high. For example, the solubility of aniline dodecylbenzene sulfonate in toluene or xylene is at most 0.5%. Thus, a method for producing polyaniline having a further higher solubility is sought. Further, a conductive polymer composition composed of a substituted or unsubstituted polyaniline, a protonic acid and an organic solvent has been reported (Japanese Unexamined Patent Publication (Kokai) No. 2003-176409), but since the oxidizing agent/aniline (molar ratio) at the time of polymerization of the aniline is 0.5, there is the problem that the yield of the polyaniline is 30% to 40%. When a molar ratio of an oxidizing agent/aniline is 1.0 or more, the dispersion stability becomes insufficient. Further, attempts are being made to improve the solubility by introducing a substituent into the side chain of the aniline, but this is not for general use products, the yield is low and the conductivity is decreased, and therefore, this proposal is not preferred. The solubility and dissolution of the polyaniline or polyaniline derivative in an organic solvent referred to here indicates coexistence of the state where fine particles of polyaniline or a polyaniline derivative are dispersed in an organic solvent and the state where polyaniline or a polyaniline derivative is dissolved in an organic solvent.
A photovoltaic device is composed of a photoelectrode and a counter electrode. In the past, as the counter electrode, an electrode composed of a platinum thin film formed on a transparent conductive glass substrate by vacuum vapor deposition or sputtering has been used. However, vacuum vapor deposition or sputtering requires expensive vacuum equipment. Further, the size of the substrate is strictly restricted, so it is difficult to form a platinum layer on a substrate of a large area.
The dye-sensitized solar cell was developed by Graetzel et al. of Switzerland. Among solar cells using organic materials, it has the advantages that it is high in photovoltaic conversion efficiency and is lower in manufacturing cost compared with silicon-based solar cells and, therefore, is gaining attention as a new type of solar cell.
FIG. 1 shows an example of the typical configuration of a dye-sensitized solar cell. Typical examples of a dye-sensitized solar cell include, a ruthenium complex dye-sensitized type titanium dioxide solar cell. Explaining the configuration of a cell taking, as an example, this ruthenium complex dye-sensitized type titanium dioxide solar cell, shown in FIG. 1, a transparent substrate 11 such as glass is provided on one surface with a transparent conducting layer 12. On the top thereof, an oxide semiconductor mesoporous film 13 is formed comprising oxide semiconductor particles such as titanium dioxide and carrying a photosensidizing dye (e.g., a ruthenium complex dye) to form a photoelectrode 14. A counter electrode 15 is arranged facing the photoelectrode 14. It is possible to arrange the electrolyte layer 16 comprising an electrolyte comprising non-aqueous solution containing a redox of iodine/iodine ion, etc. between the photoelectrode 14 and counter electrode 15.
In this dye-sensitized solar cell, when sunlight or other light strikes the cell from the transparent substrate 11 side, electromotive force is generated between the photoelectrode 14 and counter electrode 15, electrons flow from the photoelectrode 14 to the counter electrode 15, and power is generated. The counter electrode 15 comprising a conductive substrate such as, metal substrate or a non-conductive substrate such as glass substrate on which a conducting layer such as platinum, gold, carbon is formed, or a non-conductive substrate such as glass substrate on which a conductive metal oxide film and a conducting layer such as platinum, gold, carbon, are formed, or on a nonconductive substrate such as a glass substrate, a conductive metal oxide film such as fluorine-doped tin oxide (FTO) and tin-doped indium oxide (ITO) and a conductive film such as platinum, gold and carbon are successively laminated. In particular, platinum has large catalytic action enabling smooth injection of electrons from the counter electrode 15 to the electrolyte 16, so a counter electrode 15 having a platinum thin film is much used.
A counter electrode 15 having a platinum thin film has conventionally been obtained forming a platinum thin film on a substrate by vacuum vapor deposition or sputtering (Japanese Unexamined Patent Publication (Kokai) No. 2000-173680 and Japanese Unexamined Patent Publication (Kokai) No. 2000-36330). However, platinum is an expensive precious metal more expensive than gold. When using sputtering or vacuum vapor deposition to form a counter electrode 15 having a platinum thin film, there is much waste in the consumption of materials, the productivity is low, a vacuum facility is required, the capital cost is high and the production cost becomes higher. Alternatively, a counter electrode 15 having a platinum thin film may be formed by a method of dipping a substrate into a platinum solution such as chloroplatinic acid solution to coat the substrate with the platinum solution, then sintering it or by coating a platinum solution on a substrate by spraying, then sintering it. Both dipping and spraying may also be mentioned as simple methods, since they do not require vacuum facilities, but to convert a platinum solution coated on a substrate to a platinum thin film, sintering at about 400° C. is required, so there was the defect that this method cannot be applied to a substrate weak against heat.
Further, a counter electrode formed with a conductive polymer thin film, instead of a platinum thin film, has also been reported (Japanese Unexamined Patent Publication (Kokai) No. 7-226527). As a method of forming a conductive polymer thin film, the method of using electrochemical polymerization to form a conductive polymer thin film on a conductive substrate or the method of coating a conductive polymer dispersion or solution on a substrate may be exemplified. Regarding the “conductive polymer solution” mentioned herein, the co-existence of the state of conductive polymer particles dispersed in a solvent and the state of a conductive polymer dissolved in a solvent is defined as a “conductive polymer solution” for brevity. Regarding the electrochemical polymerization, since the substrate which can be used is restricted to a conductive substrate or the area of the substrate which can be used is restricted, it is difficult to form a large area conductive polymer thin film on the substrate. Further, as a conductive polymer particle dispersion or conductive polymer solution, for example, an aqueous poly(3,4-ethylenedioxythiophene) dispersion (Baytron P made by Bayer), an aqueous polyaniline solution (Aquasave made by Mitsubishi Rayon), etc. may be exemplified. However, the synthesis of a monomer is troublesome. Further, as a polyaniline solution, an N-methylpyrrolidone solution of a polyaniline has been reported, but the method of preparation of the solution was troublesome or, since the polyaniline thin film obtained from a polyaniline solution is an insulator, an operation for doping to convert it to a conductor is necessary and not simple (Japanese Unexamined Patent Publication (Kokai) No. 3-28229 and U.S. Pat. No. 5,728,321). Further, an organic solvent dispersion of a conductive polyaniline has been reported in the Japanese Unexamined Patent Publication (Kokai) No. 6-279584 or Japanese Unexamined Patent Publication (Kokai) No. 2003-277500, but the dispersability to an organic solvent is not necessarily high (Japanese Unexamined Patent Publication (Kokai) No. 6-279584) or the method of preparation of the dispersion was troublesome. Further, the conductive polymer thin film formed with the conductive polymer particle dispersion or conductive polymer solution does not exhibit a performance as good as a platinum thin film.